1. Field of the Invention
The present invention relates to a method of adjusting a ring resonator and, more particularly, to a method of exactly adjusting the resonance frequency of the ring resonator.
2. Prior Art
Ring resonators, for example for narrow band filters and for constructing resonators for microwave oscillators, formed as strip lines, are known, for example, from the article by U. Karacaoglu, I. D. Robertson and M. Guglielmi, entitled xe2x80x9cAn Improved Dual-Mode Microstrip Ring Resonator Filter with Simple Geometryxe2x80x9d, 24th European xe2x80x9cMicrowave Conferencexe2x80x9d, 1994, pp. 442 to 447, and the article by H. Yabuki, M. Sagawa, M. Matsuo and M. Makimoto, entitled xe2x80x9cStripline Dual-Mode Ring Resonators and Their Application to Microwave Devicesxe2x80x9d, IEEE Transactions on Microwave Theory and Techniques, Vol. 44, No. 5, May 1996, pp. 723 to 729. For those applications the desired resonance frequency at which the ring resonator should oscillate to filter a narrow frequency band must be adjusted very accurately. These printed ring resonators usually have material variations and manufacturing tolerances, especially at higher frequencies, since the manufacturing tolerances produce greater effects because of the smaller dimensions of the ring resonator. A printed ring resonator thus usually has a resonance frequency which is not exactly equal to the predetermined desired resonance frequency. An adjustment of the resonance frequency must occur subsequently in which the Q or quality factor of the resonator may be impaired only insignificantly. It is very important for the electrical properties of the oscillator and/or filter that the Q of the resonator be kept as high as possible.
It is an object of the present invention to provide a method for very accurate adjustment of a resonance frequency of a ring resonator which is formed as a strip line ring, which is as simple and easy to perform as possible.
These objects, and others which will be made more apparent hereinafter, have been attained in a method for adjusting a resonance frequency of a ring resonator, which is formed as a strip line ring.
According to the invention, conducting material is removed with a laser at one or more positions on the strip line ring or a strip line coupled to this strip line ring, until a desired predetermined resonance frequency is reached. This method attains the above object of the invention.
A very accurate adjustment of the resonance frequency of ring resonators formed in strip line engineering may be performed using the method according to the invention, since the conductive material can be removed in arbitrarily small portions by means of a laser. Because of these adjusting processes it is possible to allow greater manufacturing tolerances and fluctuations in material parameters, whereby a considerable cost reduction is attained. The geometric structure of the resonator is only changed slightly by the laser adjustment so that the resonance quality is only slightly reduced. For use in oscillators and filters as high as possible a quality factor is required.
According to preferred embodiments of the invention conducting material is removed at positions on the strip line ring at which current maxima occur in order to reduce the resonance frequency, or at positions at which current minima occur in order to increase the resonance frequency.
In various preferred embodiments the conducting material is appropriately removed in the form of a slot narrowing or reducing the conductor width of the strip line ring. A gross adjustment of the resonance frequency can be obtained by varying the depth of the slot. A fine adjustment of the resonance frequency occurs by changing the width of the slot. In the strip line coupled with the strip line ring either material is removed to shorten its length or to reduce its width at one or more positions.